1. Field of the Invention
The present invention relates to phase change memory, and more specifically to content addressable memory utilizing phase change memory and separate word-line and search-line access elements.
2. Description of Background
Content addressable memory (CAM) is a type of computer memory utilized in high speed searching applications. Most CAM devices utilize static random access memory (SRAM) as data storage devices (utilizing transistors to store data) and access transistors for match operations. Often in these CAM devices the access transistors large and power-intensive field effect transistors (FET).
Phase change material can also be utilized to store data for CAM devices. Information is stored in materials that can be manipulated into different phases. Each of these phases exhibits different electrical properties that can be used for storing information. The amorphous and crystalline phases of the phase change material are typically two phases used for bit storage (1's and 0's) since they have detectable differences in electrical resistance. Specifically, the amorphous phase has a higher resistance than the crystalline phase.
Chalcogenides are a group of materials commonly utilized as phase change material. They typically contain a chalcogen (Periodic Table Group 16/VIA) and a more electropositive element. Selenium (Se) and tellurium (Te) are the two most common semiconductors in the group used to produce a chalcogenide when creating a phase change memory cell. An example of this would be Ge2Sb2Te5 (GST), SbTe, and In2Se3. However, some phase change materials do not utilize chalcogen, such as GeSb. Thus, a variety of materials can be used in a phase change material cell as long as they can retain separate amorphous and crystalline states.